Extensometers



United States Patent ce arszsss EXTENSGMETERS i Warren Peter Neni Bailey, Lymrn, England, assigncr to United Kingdom Atomic Energy Authority, London,

Engand i i Filed Apr. 19, 1963, Ser. Ne. 274,!21 Claims priority, application Great Eritan, Apr.

16,366/62 v 5 Claims. (Cl. 73-375) This invention relates to extensometers.

A known extensometer has a chamber with an inlet containing a restriction through which air at a constant supply pressure is passed. A pressure gauge is connected to the chamber, and the chamber also has an outlet orifice into which extends a tapered needle valve connected to the specimen under test. Movement of the needle valve consequent upon a dimensional change of the test specimen varies the eliective area 'of the outlet orice and ,hence the air pressure inside the chamber. In this way between the members by movement' transmitted to one of the members by a dimensional change of a test specimen varies the length of the restriction through which the fluid flows before reacbing the signal port. With pressurised fluid at a constant supply pressureted to the inlet port the fluid pressure tat the signal port is found to bear a substantially linearrelationshp to the length of the restriction traversed by the fluid in reaching the,

signal port and consequently to the dimensional change of the test specimen. i

By way of example an extensometer in accordance with the invention will now be described with reference to the accompanying drawings which shows a longitudinal View (partly in section) of an extensometer, together with associated equipment which is illustrated diagrammatically. i

In the drawing an eXtenso'meter 1 comprises a sleeve member 2 of circuiar section having at one end thereof a pressurised fluid inlet port 3, at the other end thereof an outlet port 4, and intermediate the ends a fluid-pressure signal port 5, and a cylindrical slide member 6 disposed within the member 2, the members 2, 6 dening between them a restriction 7 (shown enlarged for clarity) of uniform section over the length of the' member 6.

The inlet port 3 is formed in an end wall 3:1 of the i sleeve member 2 and has a connecting pipe 8, and the i signal port 5 is formed by a hood 9 eXtending circumg ferentially round and sealed to the outer wall of the member 2 and a plurality of circumferentially equi-spaced passages 10 extendingrfrom -a circumferential groove 11 formed in the inner wall of the member 2 to the interior of the hood 9. The port 5 has a connecting pipe 12. The slide member 6 has an intermediate portion 6a between end portions 13, 14 of reduced diameter, the end portions 13, 14 each having three circumferentially equi-spaced locating pins (one of which is shown for each ot the end portions 13, 14). One of the pins 15 on the end portion 13 (and correspondingly on the end portion 14) is lightly spring-loaded, the 'others being -rigidly ecured. "The pins 15 serve to locate the slide member 6 substantially centrally in the sleeve member 2, the inner surface of the'sleeve member 2 and the surface of the portion sa of the slide member 6' being honed so as to be of a size and finish such that the restriction 7 is 'in the form of a narrow clearance between the members 2, 6 and of uniform annularsection over the length of the portion 651 of the slide member 6. Typi-` cally the restriction 7 has a radial width of one thousandth of an inch for a diameter of the portion Ga of the slide member 6 of half an inch. The spring-loaded pins 15 serve to maintain a constant relative radialrlocation between the members 2, 6 over the whole operative travel of the member 6. The portion 14 has secured to it a coaxial feelerrod 16 extending beyond the port 4. 'A source 18 of pressurised gas is connected -to the pipe S by way of a constant pressure valve 19,

a pressure gauge 26 being provided. A pressure gauge 21 is connected to the end of the pipe 12 remote from the -varies the` length of the restriction '7 through which the gas flows before reaching the signal port 5. The pressure recorded on the gauge 21Vis found to bear a substantially linear relationship to the length of the restriction 7 traversed by the gas in teaching the signal port 5 and consequently to the dimensional change of the test specimen 17,'since the uniform section of the restriction 7 over its length ensures that the restriction of gas flow per unit length is constant.

The extensometer 1 has greater accuracy over a wider range (typically an accuracy of 0.1 to O.2% over a range of movement of one inch) than the known extensometer referred to above.

4 The invention is not limited to the details of the example described above. Thus the member 6 may be held stationary using a support extending through the port 4 (the rod 16 being dispensed with) and a dimensional change of the test specmen transmitted through another feeler rod to cause longitudinal movement of the sleeve member 2. Such an arrangernent requires thepipes 8, 12 to be flexible, and'for this reason the arrangement in which the member 6 is movable is preferred.

The invention has particular application in high temperature environments in that the simple form of the sleeve and slide members facilitates any compensation 1. An extensometer comprising a sleeve member havi i ing a signal port intermediate an inlet port and an outlet port, a slide member disposed within the sleeve member, the slide member having an intermediate portion between end' portions of reduced size located with respect to the sleeve member, and the intermediate portion defiring with the sleeve member an annular restriction to flow of fluid from the inlet port to the outlet port, the restriction being of uniforma section over the length of the intermediate portion, and means for causing relative longitudinal movement between the members consequent upon a dimensional change of a test specimen thereby Varying thelength of the restriction through which the fluid flows before reaching the signal port.

2. An extensometer as claimed in claim 1, wherein said means comprises a feeler rod Secured to one of said end portions and extendingbeyond said outlet port.

' Patented June 8, 1965 r i 3. An extensometer comprising a sleeve member having at one end an inlet port and at the other end an outlet port, the sleeve member also having a signal port intermediate the inlet and outlet ports, a slide member disposedlongitudinally within the sleeve member, the

slide member having an intermediate portion between end portions of reduced size, the end portions being disposed one to each side of said signal port and located With respect to the sleeve member, and the intermediate portion definirg With the sleeve member an annular restriction to flow of gas from the inlet port to the outlet port, the restricton being of uniform section over the length of the *intermediate portion, a feeler rod coaXial With the slide member, the rod being Secured to one of said end portions and extending beyond said outlet port for causing longitudinal' movement of the slide member relative to the sleeve member consequent upon a dimensionalcharge of a test specimen to vary the length of the res'triction through which the gas flows before reachingthe'sign al port, `meansfor feeding pressuris'ed gas at conthe annular restriction has a radial Width of one thousandth of an inch for a diameter of the intermediate portion of one half inch.

References Cited by the Examiner FOREIGN PATENTS i 23,324 7/ 49 Finland. 921998 5/ 47 France. 879,985 10/61 Great Britain.

ISAAC LISANN, Pr'mary Examner( 

3. AN EXTENSOMETER COMPRISING A SLEEVE MEMBER HAVING AT ONE END AN INLET PORT AND AT THE OTHER END AN OUTLET PORT, THE SLEEVE MEMBER ALSO HAVING A SINGLE PORT INTERMEDIATE THE INLET AND OUTLET PORTS, A SLIDE MEMBER DISPOSED LONGITUDINALLY WITHIN THE SLEEVE MEMBER, THE SLIDE MEMBER HAVING AN INTERMEDIATE PORTION BETWEEN END PORTIONS OF REDUCED SIZE, THE END PORTIONS BEING DISPOSED ONE TO EACH SIDE OF SAID SIGNAL PORT AND LOCATED WITH RESPECT TO THE SLEEVE MEMBER, AND THE INTERMEDIATE PORTION DEFINING WITH THE SLEEVE MEMBER AN ANNULAR RESTRICTION TO FLOW OF GAS FROM THE INLET PORT TO THE OUTLET PORT, THE RESTRICTION BEING OF UNIFORM SECTION OVER THE LENGTH OF THE INTERMEDIATE PORTION, A FEELER ROD COAXIAL WITH THE SLIDE MEMEBER, THE ROD BEING SECURED TO ONE OF SAID END PORTIONS AND EXTENDING BEYOND SAID OUTLET PORT FOR CAUSING LONGITUDINAL MOVEMENT OF THE SLIDE MEMBER RELATIVE TO THE SLEEVE MEMBER CONSEQUENT UPON A DIMENSIONAL CHANGE OF A TEST SPECIMEN TO VARY THE LENGTH OF THE RESTRICTION THROUGH WHICH THE GAS FLOWS BEFORE REACHING THE SIGNAL PORT, MEANS FOR FEEDING PRESSURIZED GAS AT CONSTANT PRESSURE TO THE INLET PORT AND MEANS FOR MEASURING THE GAS PRESSURE AT THE SIGNAL PORT. 